There are numerous methods available for detecting physiological signals including electroencephalograph (EEG), electrocardiograph (EKG), and electromyography (EMG) and for translating these signals into meaningful feedback to provide information to the user regarding their psychophysiological state. This is most frequently done in a controlled laboratory environment involving multiple computers and trained technical staff. In addition, the majority of the applications described involve training the user to increase or decrease simple derivative measures of EEG such as the alpha or theta bands or increasing or decreasing heart rate or a specific pattern of muscle activity.
It is theorized that each of the major sub-bands of biofeedback EEG (delta, theta, alpha, beta) correspond with unique subjective characteristics of an individual. The delta band is observed most clearly in deep sleep, the theta band in light sleep and drowsiness, the alpha band in a variety of wakeful states involving creativity, calm and inner awareness, and the beta band in alert wakeful situations with external focus. One problem with laboratory based feedback training is that it is conducted in a constrained environment with relatively limited number of stimuli, situations or tasks that the subject is supposed to learn how to handle. Specifically, training is typically confounded with few distracters that tend to be perceived as artificial and become predictable after some time spent in the lab. In effect, the knowledge gained or skills learned may not transfer well to real-world applications and the retention times are short. Repeated visits to the laboratory are then required for the user to maintain the control over physiological states.
Many different approaches have been taken to EEG biofeedback to achieve mental state control. For example, U.S. Pat. No. 4,928,704 describes a biofeedback method and system for training a person to develop useful degrees of voluntary control of EEG activity. EEG sensors are attached to cortical sites on the head for sensing EEG signals in a controlled environmental chamber. The signals are amplified and filtered in accordance with strict criteria for processing within time constraints matching natural neurological activity. The signals are filtered in the pre-defined bands of alpha, theta, beta and delta, and fed back to the monitored person in the form of optical, aural or tactile stimuli. In another example, U.S. Pat. No. 4,949,726, U.S. Pat. No. 5,024,235, and U.S. Pat. No. 5,406,957 describe an EEG Neurofeedback apparatus for training and tracking of cognitive states which measures bioelectric signals in bandwidth windows to produce a composite amplitude by a fast Fourier transform on an amplified signal. Selected bandwidths are displayed and monitored by computer to enable training of a person being monitored with audio or verbal feedback. All these systems are lab-based, and cannot be applied in the field. In addition, the definition of desired or target mental states is given ‘ad hoc’ without any reference to mental states of subjects who are considered experts in a task at hand.